1. Field of the Invention
This invention relates to compositions and methods for inhibiting corrosion of copper and aluminum surfaces in fuel systems, and more particularly to such compositions and methods for inhibiting corrosion of copper and aluminum surfaces in petroleum-based fuel systems which contain elemental sulfur or sulfur-containing compounds, such as mercaptans.
2. Prior Art
A problem commonly encountered during production, storage and handling of many petroleum-based fuels is corrosion of copper and aluminum surfaces contacted by the fuel. Such corrosion is undesirable not only because of the resulting deterioration of such surfaces, but also because aluminum and copper particles are thereby released into the fuel, tending to exacerbate degradation of the fuel. The copper corrosion is known to be encouraged by presence in the fuel of sulfur in elemental or compound form. Moreover, the problem of corrosion has been aggravated recently by increased use of fuels containing alcohol additives such as ethanol. Alcohol/fuel mixtures, such as "gasohol", tend to absorb and retain higher concentrations of water than does alcohol-free petroleum-based fuel, thereby increasing the rate of corrosion, particularly of aluminum.
Conventionally, thiadiazole derivatives have been incorporated into fuel and other systems to inhibit corrosion of metal surfaces in the system. Such corrosion inhibitors generally have been effective in inhibiting corrosion caused or enhanced by the presence of certain sulfide-type sulfur-containing compositions, such as hydrogen sulfide, in fuel and other systems. However, such inhibitors have been found to be less effective against corrosion catalyzed by the presence of elemental sulfur and sulfur-containing compounds such as mercaptans. Many commercially available fuels, such as diesel fuel, jet fuel and gasoline, tend to contain significant concentrations of elemental sulfur and mercaptans, while such fuels generally tend not to contain significant concentrations of the sulfide-type compositions to which the prior art inhibitors are directed. Sulfide-type compositions are substantially removed from the fuel during standard refinement and processing of the fuel. Accordingly, the inadequacy of the commercial inhibitors in inhibiting copper or aluminum corrosion resulting from elemental sulfur and mercaptans is a serious drawback.
Benzotriazole has been used as a corrosion inhibitor in aqueous systems. For example, as noted in Chem. Abstr. 88:25475p, benzotrizole and mercaptobenzothiazole have been employed in aqueous ethylene glycol solutions to inhibit corrosion on certain surfaces exposed to such antifreeze solutions. In view of the relative insolubility of benzotrizole in oil, its use generally has been limited to aqueous systems. However, benzotrizole has been incorporated in combination with a higher fatty amide of a polybasic amine in leaded gasoline to inhibit corrosion of lead containers. See Chem. Abstr. 84:62205p.
Aside from the oil-insolubility limitation, benzotriazole also has been found to be undesirable as a corrosion inhibitor in fuel systems for several other reasons. Incorporation of benzotriazole into fuel tends to darken the fuel; and dark fuels are viewed by many customers as undesirable. In addition, water tends to separate out of fuel held in storage tanks, thereby forming a water/fuel two-phase system. Since benzotriazole has a higher water solubility than oil solubility, it tends to separate out of the fuel and into the water phase, thereby limiting its effectiveness in inhibiting corrosion of surfaces contacted by the fuel.
U.S. Pat. No. 4,197,210 describes the use of an adduct of benzotriazole with dialkylene amines in lubricating oils. In such oils, corrosion problems typically result from the presence of sulfide-type compositions included in the lubricating oil for a variety of functions, including anti-oxidant, lubricity, and high-pressure wear functions.
Accordingly, a need has existed for oil-soluble fuel additives which inhibit copper and aluminum corrosion caused or enhanced by the presence of elemental sulfur or mercaptans, and for such additives which will not turn fuel dark or tend to separate out of fuel in a fuel/water two phase system.